Many refrigeration systems are required to provide cooling without necessarily having access to a continuous supply of electricity. In some cases electrical power is not available for large parts of the day in remote areas or for mobile systems. In others, the systems are required to avoid consumption of power during peak periods. Conventional eutectic systems have been developed to operate under these circumstances, but do not provide adequate temperature control for many purposes. Solar power systems with storage batteries have been developed but are relatively expensive and cannot guarantee that electricity will be available.